Wide track vehicle

ABSTRACT

A wide track vehicle with improved skid steering by having a chassis (1) supported upon two independently drivable tracks (2) by side support wheels (3) engaged with each track adjacent the outer edges only. Downwardly projecting rubbing strips (11, 12, 13) are attached to the underside of the chassis (1) to engage slideably with each track only when the track is upwardly deflected by uneven terrain. The tracks (2) each rotate upon a plurality of full width direction-changing rollers attached to the chassis and each having a rolling surface which is provided with mud-cutting, helical ridges (18).

TECHNICAL FIELD OF THE INVENTION

This invention relates to a tracked vehicle suitable for unmanneddeployment in hostile environments.

BACKGROUND ART

The mobility of an unmanned vehicle is extremely dependent upon theterrain, obstacles in the path of the vehicle causing various mobilityfailures such as overturning, gross slippage, nose-in failure andhang-up failure, the latter two being caused by engagement of the noseand belly respectively of the vehicle with the terrain.

Wide track manned vehicles having tracks extending substantially thefull width of the vehicle are known for use on relatively even terrain.The tracks of such vehicles fully cover the belly and hence would besuitable for eliminating the possibility of hang-up failure were it notfor the steerage problems engendered in use on uneven terrain by themode of steering that has to be employed, ie skid steering.

Skid steering comprises the application of a velocity differential tothe two independently drivable, parallel tracks of the vehicle, whichapplication causes the tracks to skid about a pivot axis trajectory, thelocation of which is determined both by the velocity differentialapplied and by the load distribution of the vehicle upon the tracks.When the tracks are wide and the terrain is uneven it becomes difficultto predict where ground contact will take place, with consequentunpredictability of loads and rates of turn during steering.

The present invention seeks to provide a wide track vehicle withimproved skid steering on uneven terrain.

THE INVENTION

Accordingly, the present invention comprises a tracked vehicle having achassis supported on two independently drivable, parallel tracks,together extending substantially the full width of the chassis so as tocover substantially the whole belly thereof, wherein the chassis issupported upon a plurality of side support wheels, engageable with aninner face of each track adjacent the outer edge thereof, at least onelongitudinally disposed rubbing strip being located inwardly of eachplurality of support wheels and having less downward projection than thesupport wheels, thereby to be slideably engageable with the inner faceof the track only when the underlying track is upwardly deflected byuneven terrain.

Preferably a parallel plurality of the said rubbing strips is providedinwardly of each plurality of side support wheels, each strip being ofprogressively reducing downward projection with increasing proximity tothe centre line of the vehicle.

In order to maintain the geometry of the track, full width, directionchanging rollers are provided at each turning point of each track, ie,where the tracks change direction. Each of these full width rollers hasa rolling surface which is preferably provided with axially inclinedridges or blades in order to avoid build up of mud or clay depositsbetween the rollers due to low contact pressure.

The maximum height of obstacle that can be mounted by the vehicle is ofcourse dependent upon the length of the ground engageable portion of thetracks, ie, track-base, defined by the spacing of the lower, full width,direction changing rollers, ie the road rollers. A preferred arrangementfor unmanned use is provided with three only direction changing rollerscomprising two road rollers and one drive sprocket roller. Thisarrangement is advantageous over conventional four-roller arrangementsof manned tracked vehicles, both in providing a longer track base and inshifting the centre of gravity of the vehicle forward, thereby providinga vehicle which will behave well in either a forwards or a backwardsdirection.

Where the vehicle is intended for unmanned use, the chassis and drivemechanisms mounted thereon are contained entirely within the perimeterof the tracks. Access to the drive mechanisms may be achieved by adrawer system, ie the various components being slideably mounted onrunners transverse to the longitudinal centre line of the vehicle. Thechassis may also be enclosed within a body and provided with a tophamper bridging the tracks, upon which various terrain sensors andcontrol units may be mounted.

SPECIFIC EXAMPLE OF THE INVENTION

An embodiment of the invention will now be described by way of exampleonly with reference to the accompanying drawings, of which

FIG. 1 is a part cut-away diagrammatic side elevation of an unmannedtracked vehicle,

FIG. 2 is a front view of the same vehicle part-sectioned on line II--IIof FIG. 1, and

FIG. 3 is a perspective view of a full width, direction changing rollerused in the vehicle of FIG. 1.

The tracked vehicle illustrated in FIG. 1 is intended for unmanned useand comprises a chassis 1 supported on each of two independentlydrivable, half width tracks 2 by four side support wheels 3 engaged withthe inner face of each track 2 adjacent the outer edge thereof. Eachtrack 2 rotates about three full width direction changing rollers 4, 5and 6, the two lower rollers 4 and 5 defining a track base 7 and theupper roller 6 comprising a drive sprocket roller disposed forwardly ofthe lower roller 4.

Each side support wheel 3 is attached to the chassis 1 by a pivoted arm8 and urged against the track 2 by a suspension member 9 and acompression spring 10.

Attached to the underside of the chassis 1 inwardly of each set of sidesupport wheels 3 are three longitudinally extending, low friction,rubbing strips 11, 12 and 13, each having a progressively reduceddownward projection with increased proximity to the centre line of thevehicle. These rubbing strips 11, 12 and 13 carry the vehicle load onlywhen crossing an obstacle, ie when the tracks 2 are deflected upwardlyby an underlying obstacle interjacent the two sets of side supportwheels 3, each strip coming consecutively into engagement with the track2 as track deflection is increased by the obstacle.

The chassis 1, which is disposed entirely within the periphery of thetracks 2, supports a body 14 within which drive mechanisms (not shown)for the drive sprocket rollers 6 are contained. The body 14 also carriesa top hamper 15 bridging the two tracks 2, upon which top hamperelectronic drive control means 16 are mounted together with any otherancillary equipment that may be required for specific applications ofthe unmanned vehicle.

The control means 16 includes sensors, analysers and motivators (notshown) arranged either for remote command or for command by apre-programmed computer also included in the control means 16, so as tomake the vehicle autonomous.

The vehicle is steered by application of a velocity differential to thetwo independently drivable tracks 2, ie by conventional skid steeringbut, because the weight of the vehicle is carried only at the outer edgeof each track in normal running, the steering is more predictable thanthat of conventional wide track vehicles.

The concentration of vehicle loading onto the side support wheels 3engenders low contact pressure between the full width, directionchanging rollers 4 and 5 and the track, a condition which permits mud topack between the track and the roller, leading to track throwing ifallowed to prevail.

A solution to this problem is illustrated in FIG. 3, which figuredepicts a direction changing roller 4/5 having a rolling surface 17provided with a plurality of mud cutting, helical ridges 18 engaged withthe track 2. These ridges 18 provide a reduced contact area with thetrack 2 and a consequently increased contact pressure over that area,enabling the ridges to cut through any mud deposits interjacent theroller and the track. The helical form of the ridges 18 ensures that thethus partitioned deposits are ejected, by rotation of the roller, fromthe ends of the roller.

The embodiment of the invention herein described is an unmanned vehiclesuitable for a range of purposes such as decoy, surveillance, supply orsentry duties in hazardous environments. However it will be obvious tothose skilled in the art that the invention is also advantageouslyapplicable to manned, wide track vehicles in order to improve thepredictability of skid-steering.

We claim:
 1. A tracked vehicle having a chassis (1) supported on twoindependently drivable, parallel tracks (2), together extendingsubstantially the full width of the chassis so as to cover the bellythereof, wherein the chassis (1) is supported upon a plurality of sidesupport wheels (3) engageable with an inner face of each track adjacentthe outer edge only thereof, at least one longitudinally disposedrubbing strip connected to the belly of the vehicle chassis beinglocated inwardly of each plurality of support wheels (3) and having lessdownward projection than the side support wheels, thereby to beslideably engageable with the inner face of the track only when theunderlying track is upwardly deflected by uneven terrain.
 2. A trackedvehicle as claimed in claim 1 wherein the chassis (2) is provided with aparallel plurality of the said rubbing strips (11, 12, 13) locatedinwardly of each plurality of side support wheels (3), each strip beingof progressively reduced downward projection with increased proximity tothe centre line of the vehicle.
 3. A tracked vehicle as claimed in claim1 wherein each track (2) rotates upon a plurality of full width,track-direction-changing rollers (4, 5) each having a rolling surface(17) provided with a plurality of helical, mud cutting ridges (18)engageable with the said inner surface of the track (2).
 4. A trackedvehicle as claimed in claim 2 wherein each track (2) rotates upon aplurality of full width, track-direction-changing rollers (4, 5) eachhaving a rolling surface (17) provided with a plurality of helical, mudcutting ridges (18) engageable with the said inner surface of the track(2).
 5. A tracked vehicle having a chassis supported on twoindependently drivable, parallel tracks, together extendingsubstantially the full width of the chassis so as to cover the bellythereof, wherein the chassis is supported upon a plurality of sidesupport wheels engageable with an inner face of each track adjacent theouter edge only thereof, a plurality of longitudinally disposed,laterally spaced, parallel rubbing strips being located inwardly of eachplurality of support wheels and having less downward projection than theside support wheels, each strip being of progressively reduced downwardprojection with increased proximity to the centre line of the vehiclethereby to be slideably engageable with the inner face of the track onlywhen the underlying track is upwardly deflected by uneven terrain.
 6. Atracked vehicle as claimed in claim 5 wherein each track rotates upon aplurality of full width, track-direction-changing rollers each having arolling surface provided with a plurality of helical, mud cutting ridgesengageable with the said inner surfaces of the track.
 7. A trackedvehicle having a chassis supported on two independently drivable,parallel tracks, together extending substantially the full width of thechassis so as to cover the belly thereof, wherein the chassis issupported upon a plurality of side support wheels engageable with aninner face of each track adjacent the outer edge only of each track suchthat the weight of the vehicle is principally carried only at the outeredge of each track in normal running on relatively even terrain and thetrack portions inwardly of the support wheels and extending to the inneredges of the tracks are substantially unsupported against upwardmovement so as to be deflected upwardly when passing over uneventerrain, at least one longitudinally disposed rubbing strip beinglocated inwardly of each plurality of support wheels and having lessdownward projection than the side support wheels, thereby to beslideably engageable with the inner face of the track only when theunderlying track is upwardly deflected by uneven terrain.